1. Field of the Invention
The present invention relates to an exhaust gas return system for an internal-combustion machine, in particular a diesel engine, for returning exhaust gas produced in the internal-combustion machine to fresh air to be supplied to the internal-combustion machine. Further, the invention relates to a method of returning exhaust gas, wherein the exhaust gas of the internal-combustion machine can be returned to the fresh air used for the internal-combustion machine.
2. Description of Related Art
Conventional exhaust gas return systems comprise a piping system extending from an outlet of an internal-combustion machine to an inlet. For this purpose, the exhaust gas return system comprises a low-pressure supply line extending from an inlet to a compressor. A high-pressure supply line extends from the compressor to the internal-combustion machine for supplying fresh air aspirated at the inlet to the internal-combustion machine, in particular a combustion engine. After combustion in the internal-combustion machine, the exhaust gas produced in the internal-combustion machine is fed via a high-pressure exhaust gas line from the internal-combustion machine to a turbine. From the turbine, the exhaust gas is fed via a low-pressure exhaust gas line to an outlet. To reduce the amount of harmful substances of the exhaust gas and improve the combustion process in the internal-combustion machine, a low-pressure return line connected with the low-pressure exhaust gas line and the low-pressure supply line is provided, said low-pressure return line supplying part of the exhaust gas to the low-pressure supply line, whereby part of the exhaust gas is returned.
Such an exhaust gas return system has a drawback in that in particular during the cold start phase of the internal-combustion machine, the temperature of the fresh air to be supplied to the internal-combustion machine is not optimally adjusted and reaches the value required for satisfactory combustion only after some time. This results in unfavorable combustion in the internal-combustion machine such that, in particular in a diesel engine, the exhaust gas contains large portions of soot particles and entrained oil.
For reducing the cold start phase it is common practice to return the hot exhaust gas from the internal-combustion machine via a high-pressure return is line to the high-pressure supply line. Thus however the soot particles and entrained oil contained in the exhaust gas are returned to the internal-combustion machine such that unwanted contaminants are concentrated in the internal-combustion machine, whereby the combustion process in the internal-combustion machine is deteriorated. Further, this leads to higher wear of the internal-combustion machine, in particular in the area of the inlet valves, and to fouling of swirl flaps. In particular, the soot particles are critical for the cylinder bores of the internal-combustion machine.